In line with the development in advanced technology areas such as portable electronic devices including digital cameras, cellular phones, and notebook computers, and high-power hybrid vehicles, research into secondary batteries, which are chargeable and dischargeable, has been actively conducted as their power sources instead of non-rechargeable primary batteries.
Secondary batteries may include nickel-cadmium batteries, nickel-metal hydride batteries, nickel-hydrogen batteries, and lithium secondary batteries, and among these batteries, application areas of lithium secondary batteries tend to be rapidly increased as the lithium secondary batteries are known to have operating voltages that are three times (3.6 V) or more higher than those of typical nickel-cadmium batteries and nickel-metal hydride batteries, and excellent energy density characteristics per unit weight.
In order to stably use these lithium secondary batteries over a prolonged period of time, there is a need to suppress the formation of dendrites which are formed in an acicular shape on the surface of an anode. The dendrites are formed by the precipitation of metal foreign matters (iron (Fe), copper (Cu), nickel (Ni), cobalt (Co), manganese (Mn), zinc (Zn), tin (Sn), zirconia (Zr), etc.) on the surface of the anode while the metal foreign matters formed from an electrode during the preparation of a cell are oxidized. The dendrites may not only degrade the cycle performance of a battery, but also may increase a cell failure rate and may cause an internal electrode short circuit while the dendrites connect cathode and anode to each other by penetrating through a separator due to external pressure or vibration. Thus, the dendrites may reduce the safety of the cell.
Therefore, in order to prepare a lithium secondary battery having improved safety and stability, there is a need to develop a secondary battery that may suppress the formation of dendrites connecting cathode and anode.